1. Field of the Invention
The present invention relates to an opening structure, and more particularly, to an opening structure having a metal layer filled in an opening, and the sidewall of the opening is covered with a dielectric thin film.
2. Description of the Prior Art
The trend to micro-miniaturization, or the ability to fabricate semiconductor devices with feature size smaller than 0.065 micrometers, has presented difficulties when attempting to form contact holes (especially for high aspect ratio contact holes) in a dielectric layer to expose underlying conductive regions.
Please refer to FIGS. 1-4. FIGS. 1-4 are schematic, cross-sectional diagrams showing the process of forming contact holes in accordance with the prior art method. As shown in FIG. 1, a metal-oxide-semiconductor (MOS) transistor device 20 is formed on a semiconductor substrate 10. The MOS transistor device 20, which is isolated by shallow trench isolations (STIs) 24, includes source/drain regions 12, a gate electrode 14, and a spacer structure 16 disposed on the sidewalls of the gate electrode 14. The semiconductor substrate 10 further includes a contact etch stop layer (CESL) 32 deposited over the MOS transistor device 20 and the semiconductor substrate 10, and an inter-layer dielectric (ILD) layer 34 deposited on the contact etch stop layer 32. Subsequently, a bottom anti-reflective coating (BARC) layer 36 is deposited on the ILD layer 34. Then, a photoresist layer 40 is formed on the BARC layer 36, and a conventional exposure-and-development process is carried out to form openings 42 in the photoresist layer 40 to define the locations of contact holes to be formed later.
As shown in FIG. 2, using the photoresist layer 40 as an etching hard mask to etch the exposed BARC layer 36 and the ILD layer 34 through the openings 42 so as to form openings 44. The etching of the ILD layer 34 stops on the contact etch stop layer 32. Subsequently, as shown in FIG. 3, using the remaining photoresist layer 40 and the BARC layer 36 as an etching hard mask to etch the exposed contact etch stop layer 32 through the openings 44, thereby forming contact holes 46. As shown in FIG. 4, the remaining photoresist layer 40 and the BARC layer 36 over the ILD layer 34 are removed.
The above-described prior art method of forming contact holes has several drawbacks. First, when etching the CESL layer 32, the contact profile is also impaired due to the low etching selectivity between the ILD layer 34 and the contact etch stop layer 32. Second, the ILD layer 34 and the underlying CESL layer 32 are etched in-situ, without removing the photoresist layer 40. The polymer residue produced during the etching of the ILD layer 34 and the CESL layer 32 results in a tapered profile of the contact hole 46, thereby reducing the exposed surface area of the source/drain regions 12 and increasing the contact sheet resistance.
In light of the above, there is a need in this industry to provide an improved method of fabricating contact holes in which the contact sheet resistance is reduced without affecting the contact hole profile formed in the ILD layer.